Bottom hole assembly fiber optic shape sensing

ABSTRACT

One or more of these thermomechanical properties of an underground formation can be monitored using a monitoring system. An example monitoring system includes a signal processing module, a visualization module, a signal source module, a signal detection module, and one or more optical fibers. Each fiber includes one or more sensors. The signal source module emits an optical signal into one or more optical fibers. The one or more sensors along the fiber interact with the optical signal, and alter the optical signal in response to one or more detected thermomechanical properties. The resulting optical signal is detected by the signal detection module. Based on the detected optical signal, the signal processing module determines the one or more thermomechanical properties that were detected by the sensors. An operator can view and monitor the detected thermomechanical properties using the visualization module.

TECHNICAL FIELD

This invention relates to well construction, and more particularly to monitoring properties of down-hole tools during the construction of a well.

BACKGROUND

Wells are commonly used to access regions below the earth's surface and to acquire materials from these regions, for instance during the location and extraction of petroleum oil hydrocarbons from an underground location. The construction of wells typically includes drilling a borehole and constructing a pipe structure within the borehole. Upon completion, the pipe structure provides access to the underground locations and allows for the transport of materials to the surface.

A variety of tools are conventionally used during well construction and monitoring systems may be used to evaluate the integrity of the tools while in use. For example, a drillstring with a bottom hole assembly (BHA) can be used to drill a borehole, and monitoring systems may be used to monitor parameters related to the integrity of the BHA during drilling in order to ensure that the BHA does not malfunction when subjected to extreme environmental conditions (e.g., high temperatures and/or pressures). These monitoring systems allow an operator to maintain down-hole tools within safe operating limits.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an example system for drilling a borehole

FIG. 2 is a schematic diagram of an example monitoring system.

FIG. 3 is a schematic diagram of an example fiber with Bragg gratings.

FIG. 4 shows light interference due to reflections in an example fiber.

FIGS. 5A-D show different views of an example BHA and fiber.

FIG. 6 shows another example BHA and fiber.

FIGS. 7A-C show different views of an example coupling member.

FIG. 8A shows an example drill collar.

FIGS. 8B-C show example arrangements of drill collars and coupling members. Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Well construction typically includes drilling a borehole and constructing a pipe structure within the borehole. For instance, as illustrated in FIG. 1, an operator can use a measure while drilling (MWD) or logging while drilling (LWD) system 100 to drill a borehole 102. The system 100 includes a surface control unit 110 and a drillstring 120.

Drillstring 120 includes a bottom hole assembly (BHA) 122 along its lower portion, and a drillpipe 128 that extends between the BHA 122 and the surface control unit 110.

BHA 122 is a component that allows drillstring 120 to drill through the surrounding medium 130, and provides the mechanical force and structural support necessary to perform a drilling operation. BHA 122 includes one or more components to provide this functionality. For example, BHA 122 includes one or more drill bits 124. Drill bit 124 is positioned at the end of the BHA 122, and includes one or more moveable drilling elements. During operation, drill bit 124 crushes, scrapes, or cuts the surrounding medium 130 through pounding or rotational motion of its drilling elements.

BHA 122 also includes one or more drill collars 126. Drill collars 126 are positioned between the drill bit 124 and the drill pipe 128, and provide structural support for the drill bit 124 and the other components of the BHA 122. Drill collars 126 are generally of a tubular shape, and allow for the passage of fluids from the drillpipe 128 to the drill bit 124 through an internal channel. Drill collars 126 also apply weight on the drill bit 124, and through their weight provide the downward force needed for drill bit 124 to efficiently drill into the surrounding medium 130.

BHA 122 can also include other components that support the operation of drillstring 120. For example, BHA 122 can include one or more motors (not shown) to operate the drill bit and/or to circulate drilling fluid.

BHA 122 is connected to the surface by drillpipe 128. Drillpipe 128 provides a conduit for the transfer of power, fluid, and/or communications signals between the BHA 122 and the surface control unit 110, and also provides a connection through which the surface control unit 100 to raise, lower, and rotate the BHA 122. Using the surface control unit 110, an operator can direct the BHA 122 along a three dimensional path (e.g., variably drilling perpendicular, horizontal, or at an intermediate angle with respect to the surface), creating the borehole 102.

During the drilling process, components of system 100 are commonly subjected to harsh environmental conditions, for instance force, pressure, temperature, and other external stressors. When the components of system 100 are exposed to these stressors, this can result in changes to the temperature of the components, changes in the shape of the components (e.g., distortions to the shape due to pressure and/or heating), and/or changes to the strain, stress, or pressure experienced by these components. In an example, the surrounding medium 130 may apply a physical force to BHA 122, which can increase the strain or stress experienced by BHA 122. In another example, the surrounding medium 130 may be hotter or colder than BHA 122, and can cause BHA 122 to heat up or cool down as it traverses through the surrounding medium 130. In another example, the surrounding medium 130 may apply a physical force to BHA 122, which can cause the BHA 122 to deform. As BHA 122 can be damaged if it experiences extreme strain, stress, pressure, and temperature, or if the BHA 122 undergoes an extreme change in shape, an operator uses a monitoring system to monitor the thermomechanical properties of the BHA (e.g., the strain, stress, and pressure experienced by the BHA 112, the shape of the BHA, or the temperature of the BHA) during operation, in order to maintain BHA 122 within safe operating limits. These operating limits typically define the conditions under which the BHA 122 can be safely operated in order to avoid damage or destruction. In general, operating limits can differ between different BHAs, and can be determined based on theoretical safety limits for a particular BHA, or can be determined empirically based on previously obtained performance information. In some implementations, the safe operating limits are used to establish thresholds for one or more of the thermomechanical properties, e.g., defining a maximum and/or minimal safe value for each thermomechanical property. One or more of these thermomechanical properties of the BHA 122 can be monitored using a fiber optic monitoring system, allowing an operator to stop or modify the operation of BHA 122 before exceeding a damage threshold for the BHA. An example fiber optic monitoring system 200 is shown schematically in FIG. 2. Monitoring system 200 includes a signal processing module 202, a visualization module 212, a signal source module 204, a signal detection module 206, and one or more optical fibers 208. Each fiber 208 includes one or more sensors 210. Signal source module 204 produces an optical signal and emits the optical signal into one or more optical fibers 208. The one or more sensors 210 along fiber 208 interact with the optical signal, and alter the optical signal based on the thermomechanical properties of the sensor 210. The resulting optical signal is detected by signal detection module 206. Based on the detected optical signal, signal processing module 202 determines information regarding the one or more thermomechanical properties of the sensors 210. This information is displayed to an operator using the visualization module 212.

When optical fibers 208 are positioned against BHA 122, such that the optical fibers 208 conform to the shape of the BHA 122 and are subject to similar environmental stressors as the BHA 122, the monitoring system 200 provides an estimate for the thermomechanical properties of the BHA 122. Thus, an operator can use monitoring system 200 to view and monitor information regarding the thermomechanical properties of the BHA 122 during the operation of the drillstring 120.

Signal source module 204 produces light and modulates the light to produce an optical signal. Signal source module 204 is coupled to fiber 208 so the produced optical signals are emitted into the fiber 208. A signal source module can produce optical signals of a single wavelength, or it can produce optical signals composed of more than one wavelength. For example, in some implementations, signal source module 204 includes one or more optical transmitters that can produce a spectrum of optical signals over a range of wavelengths. In some implementations, the optical transmitters can produce optical signals with varying data transmission rates. In some implementations, signal source module 204 is in communication with signal processing module 202, and the operation of signal source module 204 can be controlled by signal processing module 202.

Signal source module 204 includes an optical transmitter in order to produce the optical signal. Example optical transmitters include semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. In some implementations, an optical transmitter includes an LED that is made in part, for example, of Indium gallium arsenide phosphide or gallium arsenide.

Signal detection module 206 detects optical signals guided by fibers 208 and allows system 200 to interpretation of the optical signals. Signal detection module can detect optical signals over a range of wavelengths, and over a range of data transmission rates. In some implementations, signal source module 204 is in communication with signal processing module 202, and information collected by signal detection module 206 can be interpreted by signal processing module 202.

Signal detection module 206 includes an optical receiver. An optical receiver converts light into electricity using the photoelectric effect, and allows for an electric system to detect and interpret optical signals. Example optical receivers include photodetectors or other optical-electrical converters. In some implementations, a photodetector includes a semiconductor-based photodiode that is made in part, for example, of Indium gallium arsenide.

In some implementations, the functions of signal source module 204 and signal detection module 206 can be combined. For instance, a transceiver can be used to combine the optical signal transmission functions of signal source module 204 and the optical signal detection functions of signal detector module 206. In an example, a transceiver includes both an optical transmitter and an optical receiver. The optical transmitter and the optical receiver can share common components, for instance common circuitry or a common housing.

In some implementations, the monitoring system 200 can measure one or more thermomechanical properties of the BHA 122 before, during, or after the drilling process. For example, the monitoring system 200 can monitor pressure, stress, or strain experienced by the BHA 122, the shape of the BHA 122, or the temperature of the BHA 122 during a drilling operation. In some implementations, the monitoring system can gather information about one or more of these properties in real-time or near-real-time, and displays this information to an operator (e.g., an operator using surface control unit 110), such that an operator is able to continuously monitor the operation of the drillstring 120. In some implementations, the monitoring system can retain the information, so that it can be reviewed at a later time.

In some implementations, the monitoring system 200 can determine spatial information related to the thermomechanical properties. That is, the monitoring system 200 can measure a thermomechanical property, and determine the location, direction, and/or orientation of the measurement relative to the drillstring 120. As an example, monitoring system 200 can measure a localized strain experienced by a BHA 122, and can further identify the location on the BHA 122 that experienced the localized strain and the orientation of the strain measurement (e.g., whether the strain was measured from a sensor located on the top of BHA 122, the bottom of BHA 122, the side of BHA 122, and so forth).

In some implementations, the monitoring system 200 can monitor the shape of one or more components of a drill string 120. For instance, monitoring system 200 can detect the shape of the BHA 122 (e.g., the one of more drill collars 126) and/or the drillpipe 128. This allows an operator to observe the shape and relative orientation of the components of drillstring 120, so that the operator can determine if the components of drillstring 120 are positioned and arranged as expected. This also allows the operator to determine if one or more components are bending or buckling during the drilling operation, and allows the operator to determine if the drillstring 120 is bending or buckling in a manner that could damage or disable the drillstring 120. In this manner, the operator can use the monitoring system 200 to safely direct the operation of the drillstring 120.

Visualization module 212 displays information pertaining to monitoring system 200 to the operator through an operator interface. The displayed information can include, for example, one or more thermomechanical properties measured by monitoring system 200, characteristics of monitoring system 200 (e.g., the operational status of monitoring system 200 and/or one or more of its components, or the operating parameters of monitoring system 200), or other information related to the operation of system 200. Information can be displayed either as textual information, graphical information, or a combination of textual and graphical information. For example, an operator interface can display information in the form of tables (e.g., a table of thermomechanical properties), charts (e.g., a chart of thermomechanical properties over time), or images (e.g., an image illustrating locational information about one or more thermomechanical properties, or an image illustrating the shape of the components of the drillstring).

In some implementations, signal processing module 202 sends a signal to the operator interface in order to alert the operator when a measured property crosses a particular threshold, for example a known safety threshold. For instance, if the measured property has not crossed the threshold, the signal processing module 202 sends an appropriate signal to the operator interface, and the operator interface provides an indication that the BHA 122 is operating safely. If the measured property is close to crossing the threshold, the signal processing module 202 sends an appropriate signal to the operator interface, and the operator interface provides an indication that the BHA 122 is approaching its safety limits. If the measured property crosses the threshold, the signal processing module 202 sends an appropriate signal to the operator interface, and the operator interface provides an indication that the BHA 122 has exceeded its safety limits. As an example, if the measured shape of the BHA 122 cross a particular threshold (e.g., if its curvature exceeds a particular curvature threshold), the signal processing module 202 sends a signal to the operator interface, and the operator interface provides an indication that the shape of the BHA 122 has exceeded its safety limits.

In some implementations, the signal processing module 202 provides recommendations to the operator interface that assist the user in maintaining BHA 122 within safe operating limits. For example, if a measured property is close to crossing a safety threshold, the signal processing module 202 provides recommendations to the operator interface on how to avoid unsafe operation (e.g., recommendations to retract the drillstring 120, cease or slow down drilling operations, or change other aspects of the operation of drillstring 120). If the measured property crosses the safety threshold, the signal processing module 202 provides recommendations to the operator interface on how to avoid further unsafe operation. These recommendations can be displayed to the user for review.

The signal processing module 202 and operator interface can provide safety indications and recommendations based on the most recently obtained measurement, or based on a historical trend of multiple measurements. In an example, in some implementations, the signal processing module 202 and the operator interface provide an indication that the BHA 122 is returning to safe operating limits when it determines that a property is descending at a rate that would bring it below the threshold within a particular period of time, and provide a recommendation to continue the current operation. In another example, signal processing module 202 and the operator interface provide an indication that the BHA 122 is operating in an unsafe manner if the signal processing module 202 determines that a property is ascending at a rate that will exceed the threshold within a particular period of time, and provide a recommendation to cease the current operation.

In some implementations, the system can automatically (i.e., without further input from an operator) shut down or otherwise modify the operation of the BHA when a safety threshold is exceeded.

Visualization module 212 can include one or more display devices for representing information to an operator, for instance status indicators (e.g., lights that illuminate to indicate information), or a video display, such as a flat panel display (e.g., a liquid crystal display (LCD) monitor). In some implementations, visualization module 212 is located at surface control system 110, so that an operator can view information pertaining to monitoring system 200 during the operation of drillstring 120.

Monitoring system 200 can detect thermomechanical properties in various ways. For instance, sensors 210 may be Fiber Bragg Grating (FGB) sensors that can provide measurements at one or more discrete points along fiber 208. Referring to FIG. 3, an example FGB sensor 210 includes multiple Bragg gratings 302 positioned with a period of X, (i.e., the wavelength of the FBG sensor) along the length of a single-mode optical fiber 208 (i.e., an optical fiber that carries a single ray of light).

In some implementations, fiber 208 include a smaller inner core (e.g., about 4 to 9 μm in diameter) and an outer part (i.e., a cladding) of a larger diameter (e.g., about 125 μm in diameter). The inner core can be made, for instance, of glass (SiO₂), and has a high refraction index caused by high elemental doping, for instance Germanium doping. The difference in refraction indexes between the inner core and the cladding causes light to propagate only inside the inner core.

Each Bragg grating 302 has a region with a refractive index that differs from that of the fiber 208, and as a result, reflects light of a particular bandwidth at its fringe (i.e., the interface between the grating 302 and the fiber 208). For example, referring to FIG. 3, light emitted by signal source module 204 having wavelengths of λ_(a) and λ_(b) are not reflected, and are guided by fiber 208 to signal detection module 206. However, a portion of light of wavelength λ_(c) is reflected by the fringes of each Bragg grating 302 back to signal source module 204, while a portion of the light continues onto signal detection module 206. The reflection factor (i.e., the fraction of light that is reflected by each Bragg grating fringe) can be relatively small, for example between 0.001% and 0.1%.

In addition, because each Bragg grating 302 reflects light with different phase shifts, interference occurs and most of the reflected light is canceled. However, the reflections with equal phase shift accumulate to a strong reflection peak. This is illustrated in FIG. 4. The top of FIG. 4 shows a fiber 208 with a 10-fringe Bragg grating 402. Light enters from the left side of the fiber 208. Below, there are three light beams 404 a-c with different wavelengths. The upper light beam 404 a has precisely the wavelength λ₀ of the grating period and all single fringe reflections are reflected in phase, and therefore add up to a reflected energy level 406 a of ten times a single fringe reflection. The next light beam 406 b has a 10% higher frequency so that 11 light periods λ₀₊₁ have the length of the 10 grid periods λ₀. All single fringe reflections therefore have different phases and cancel, resulting in a reflected energy level 406 b of zero. A similar cancelling effect occurs with the lowest light beam 404 c, which has a 10% lower frequency so that 9 light periods λ₀₋₁ have the length of 10 grid periods λ₀, and results in a reflected energy level 406 c of zero.

As such, the bandwidth of reflection and the resulting reflected energy function is dependent on the wavelength λ of the FBG sensor. This wavelength λ is dependent on various thermomechanical properties experienced by the fiber 208. For instance, strain and temperature is related to the wavelength λ according to the following equation:

${\frac{\Delta\lambda}{\lambda_{0}} = {{k*ɛ} + {\alpha_{\delta}*\Delta \; T}}},$

where

Δλ=wavelength shift,

λ₀=base wavelength start,

k=1−p,

p=photo-elastic coefficient,

k=gauge factor,

ΔT=temperature change in K,

α_(δ)=change of the refraction index,

$\alpha_{\delta} = {\frac{\delta \; {n/n}}{\delta \; T}.}$

In an example implementation, the photo-elastic coefficient p is 0.22, the gauge factor k is 0.78, and the change of the refraction index α_(δ)is

$5 - {8*{\frac{10^{- 6}}{K}.}}$

The first expression (k*ε) of the equation describes the strain impact caused by force (ε_(m)) and temperature (ε_(T)). The second expression (α_(δ)*ΔT) describes the change of the glass refraction index n caused only by temperature.

-   -   Further,

ε=ε_(m)+ε_(T),

where

ε_(m)=mechanically caused strain,

ε_(T)=temperature caused strain,

ε_(T)=α_(sp) *ΔT,

α_(sp)=expansion coefficient per K of the specimen.

This yields the following equations which describe the behavior of an FBG sensor under the impact of both strain and temperature:

${\frac{\Delta\lambda}{\lambda_{0}} = {{\left( {1 - p} \right)*\left( {ɛ_{m} + {\alpha_{sp}*\Delta \; T}} \right)} + {\frac{\delta \; {n/n}}{\delta \; T}*\Delta \; T}}},{and}$ $\frac{\Delta\lambda}{\lambda_{0}} = {{k*\left( {ɛ_{m} + {\alpha_{sp}*\Delta \; T}} \right)} + {\alpha_{\delta}*\Delta \; {T.}}}$

In the case of a pure temperature sensor, a Bragg grating is not stressed. The FBG sensor Δλ/λ₀ signal then changes only with temperature. In this case, α is the thermal expansion coefficient α is the termal expansion coefficient α_(glass) of the fiber.

${\frac{\Delta\lambda}{\lambda_{0}} = {{\left( {1 - p} \right)*\left( {\alpha_{glass}*\Delta \; T} \right)} + {\frac{\delta \; {n/n}}{\delta \; T}*\Delta \; T}}},{or}$ ${\frac{\delta\lambda}{\lambda_{0}} = {\left( {{k*\alpha_{glass}} + \alpha_{\delta}} \right)*\Delta \; T}},$

yielding the equation for a temperature-measuring FBGS:

${\Delta \; T} = {\frac{1}{{k*\alpha_{glass}} + \alpha_{\delta}}*{\frac{\Delta\lambda}{\lambda_{0}}.}}$

The expansion coefficient α_(glass) of the fiber is very low. For example, in an example implementation, α_(glass)=0.55*10⁻⁶/K. The biggest impact results from the temperature dependent change of the refraction index α_(δ). When the fiber is fixed to a specimen, the FBG sensor signal Δλ/λ₀ changes with the strain (ε_(m)+ε_(T)) of the specimen and therefore the thermal expansion coefficient is α_(sp) then and not α_(glass). Thus,

${\frac{\Delta\lambda}{\lambda_{0}} = {{k*ɛ_{m}} + {\left( {{k*\alpha_{sp}} + \alpha_{\delta}} \right)*\Delta \; T}}},$

yielding the equation for a strain-measuring FBG sensor:

$ɛ_{m} = {{\frac{1}{k}*\frac{\Delta\lambda}{\lambda_{0}}} - {\left( {\alpha_{sp} + \frac{\alpha_{\delta}}{k}} \right)*\Delta \; {T.}}}$

When the FBG sensor is fixed to the specimen on a region without mechanical strain (ε_(m)=0), it works as temperature compensation FBG sensor. Its signal calculates according to the equations:

${\frac{\Delta\lambda}{\lambda_{0}} = {\left( {{k*\alpha_{sp}} + \alpha_{\delta}} \right)*\Delta \; T}},{{\Delta \; T} = {\frac{1}{{k*\alpha_{sp}} + \alpha_{\delta}}*{\frac{\Delta\lambda}{\lambda_{0}}.}}}$

As such, the FGB sensor can determine information the strain and temperature at discrete points along the fiber based on measurements of the reflected sensor signal, using the above relationships. Based on this information, additional information can also be determined regarding the stress at discrete points along the fiber. For instance, for materials with a known stress-strain relationship, information regarding stress can be determined as a function of the measured strain.

In some implementations, one or more wavelengths of light may be guided through fiber 208, and the FGB sensor can interact with each wavelength of light differently. In some implementations, an optical signal that includes a spectrum of light is guided through fiber 208, and the reflection spectrum is analyzed to measure multiple FBG signals simultaneously. The reflection spectrum can be analyzed, for example, using an interferometer to separate the spectrum according to the wavelengths of its component light rays.

In some implementations, FBG sensors can be used to determine the shape of the fiber 208. For example, in some implementations, a fiber 208 includes at two or more cores spaced apart, where each core includes multiple sensors 210. As described above, the sensors 210 of each core of the fiber 208 can be used to determine strain information regarding the fiber 208. If the cores are mounted such that they are non-coplanar, when fiber 208 is bent, each core will experience a different strain. The difference in strain between each core can be used to determine curvature along discrete points along fiber and can be used to determine the shape of fiber 208. By detecting strain along multiple non-coplanar cores, a multi-dimension differential strain vector can be determined. Using this differential strain vector, information about the curvature and shape of fiber 208 can be determined. In an example implementation, a fiber 208 with three non-coplanar cores can be used to determine three-dimensional shape information about the fiber 208. In some implementations, multiple fibers 208, each with single cores, can be used instead of a single fiber 208 with multiple cores. In some implementations, shape sensing can be implemented using commercially-available tools, such as using Optical Distributed Sensor Interrogator, Distributed Sensing System, or Optical Backscatter Reflectometer line of products by Luna Innovations Incorporated (Roanoke, Va.).

In some implementations, the monitoring system 200 can determine spatial information related to each of the measurements. That is, the monitoring system 200 can measure a thermomechanical property, and determine the location, direction, and/or orientation of the measurement relative to the drillstring 120. This can be implemented in various ways. For instance, in some implementations, monitoring system 200 can provide measurements from discrete points of fiber 208. If the spatial arrangement of fiber 208 is known, monitoring system 200 can use this information to determine the specific position and/or orientation of the measurement's source. As an example, if fiber 208 is known to wrap helically around a BHA 122, a measurement from a discrete point of fiber 208 can be correlated to a specific point along this helix. This point can be used to determine the location, direction, and orientation of the measurement relative to the drillstring 120. In some implementations, spatial information can be determined, in part, based on the measured shape of fiber 208.

In some implementations, instead of FBG sensors, monitoring system 200 can include other types of sensors 210, such as micro-bend sensors, interferometric sensors, polarimeter sensors, or combinations or two or more different types of sensors. For instance, sensors 210 may be micro-bend sensors. In an example implementation, when a fiber 208 is subjected to a small deformation (i.e., a “micro-bend”), light rays in the inner core of the fiber can exceed a critical angle of the inner core. This causes a redistribution of the energy between the inner core and the cladding modes. The guided higher order inner core modes couple to the cladding modes, causing the light propagating in the fiber to decrease. This mode coupling can be achieved, for instance, by placing the fiber in contact with a series of periodically positioned deformers. Hence, micro-bending causes the light intensity to decrease due to light leakage into the cladding. By monitoring and correlating the loss of light intensity, different types of micro-bend sensors can be designed which can give the measurement of the forces acting on them. In some implementations, micro end sensors are easier to implement than other types of fiber optic sensors, and can potentially be implemented at a lower cost.

Fiber 208 and its sensors 210 may be positioned on one or more components of system 100 in order to monitor the thermomechanical properties experienced by those components. For example, referring to FIG. 5A, fiber 208 may be positioned on the drill collar 126 of BHA 122. Fiber 208 can be wound around drill collar 126, for example in a helical pattern, such that it continuously wraps around the circumferential periphery of drill collar 126 as it extends the length of drill collar 126. This allows monitoring system 200 to gather information continuously along the axial length of drill collar 126, as well as continuously in radial directions surrounding drill collar 126. Fiber 208 conforms to the shape of drill collar 126, and is fixed with respect to the channel, such that any deformation of the drill collar 126 results in a corresponding deformation of the fiber 208.

Fiber 208 can be positioned within a channel 502, such that it is recessed from the outer periphery of the drill collar 126. This is illustrated in FIG. 5B, which shows the dotted region of FIG. 5A in greater detail. Like fiber 208, channel 502 can extend the length of drill collar 126, and may wind around drill collar 126 helically.

In some implementations, fiber 208 is protected by a cladding 504. For example, referring to FIGS. 5C-D, a cladding 504 surrounds fiber 208 within channel 502, protects fiber 208 from the external environment, and ensures that fiber 208 is fixed with respect to the drill collar 126. Cladding 504 can be added by any process that adds a hard material over fiber 208, for instance welding or plasma transferred arc (PTA) techniques.

Fiber 208 can connect to the other components of monitoring system 200 and system 100 in various ways. For instance, referring to FIG. 6, an example BHA 122 can include one or more drill collars 126 with a fiber 208 positioned within a channel 502 that extends along the lengths of drill collars 126. A drill collar 126 is connected on one axial end to a source sub 602, which houses the signal source modules 204 (not shown) of system 200. Source sub 602 is connected to drill collar 126 along the lower portion of BHA 122 and provides a connection point between fiber 208 and the signal source modules 204, such that an optical signal produced by the signal source modules 204 is guided along the length of fiber 208 towards the upper end of BHA 122.

The signal detection modules 206 can be positioned on the opposite end as the signal source modules 204, for example in the MWD/LWD collars 604, on another portion of drillstring 120, or on the surface (e.g., at surface control unit 110). Signal source modules 204 are connected to fiber 208 at the opposite end as signal source modules 204, and can provide information on the reflection behavior of the optical signals as it passes through fiber 208.

Signal processing module 202 can be placed in various locations, for instance along drillstring 120, or at the surface (e.g., at surface control unit 110). Signal processing module 202 is connected to signal source modules 204 and signal detection modules 206 through one or more signal transmitters (e.g., wired or wireless signal transmission connections). Signal processing module 202 controls the operation of signal source modules 204 and signal detection modules 206, and processes the optical signal in order to determine information regarding one or more properties and its associated location and orientation along fiber 208.

As shown in FIG. 6, two or more components of drillstring 120 (e.g., BHA 122) can be connected by a coupling member 606. Coupling member 606 provides a secure connection between two adjacent components, and allows fiber 208 to pass between the two components. For example, MWD/LWD collar 604 can be connected to a drill collar 126 a using a coupling member 606 a. In another example, two drill collars 126 a-b can be connected using a coupling member 606 b. In yet another example, a drill collar 126 b and the source sub 602 can be connected using a coupling member 606 c. In each of these examples, fiber 208 passes continuously across the two connected components.

Coupling member 606 is show in greater detail in FIGS. 7A-C. Coupling member 606 is generally tubular and includes a protrusion 702 at one axial end, and a recess 704 at the other axial end. Protrusion 702 and recess 704 allow coupling member 606 to be securely inserted into a component with a corresponding recess or protrusion, respectively. Coupling member 606 includes two channels 706 and 708. Channel 706 is positioned at the axial center of coupling member 606, and allows the flow of material between two interconnected components. For instance, in some implementations, when coupling member 606 b is connected between two drill collars 126 a-b, channel 706 allows for the flow of drill fluid between each of the drill collars 126 a-b. Channel 708 is positioned along a radial periphery of coupling member 606, and allows a fiber 208 to pass between two interconnected components. For instance, in some implementations, when coupling member 606 b is connected between two drill collars 126 a-b, channel 708 allows for a fiber 208 to pass between the channel 502 of a first drill collar 126 a to the channel 502 of a second drill collar 126 b. Coupling member 606 can also include one or more sleeves 710, which can slide over an ends of coupling member 606 in order to secure the connection point between coupling member 606 and a connected component.

To ensure that a fiber 208 can pass continuously between two interconnected components, one or more components can include one or more portions with reduced outer diameters. Referring to FIG. 8A, an example drill collar 126 includes an end portion 802 with a protrusion 804 that corresponds to the recess 704 of a coupling member 606. Drill collar 126 also includes a portion 806 with a reduced outer diameter relative to that of the main extension 808 of the drill collar 126. As shown in FIG. 8B, when protrusion 804 of drill collar 126 is fit into recess 704 of coupling member 606, the portion 806 remains outside of coupling member 606. This portion 806 allows for a fiber 208 to smoothly pass from channel 502 of drill collar 126 into channel 708 of drill collar 606, such that it can continuously pass between the two components. As shown as FIG. 8C, a coupling member 606 can be used in this manner to connect two components together (e.g., two drill collars 126 a-b), such that fiber 208 passes continuously between each of the connected components.

In some implementations, more than one fiber 208 may be used. For instance, a drill collar 126 can include two or more fibers 208 wrapped along its periphery. The fibers can be positioned such that they are equally spaced from each other (e.g., positioned so that they maintain a constant distance from each other along the drill collar 126), or they can be positioned in other arrangements. For example, in some implementations, fibers 208 can be positioned such that at one or more locations, fibers 208 are closer to each other than in one or more other locations. In some implementations, one or more fibers 208 are bundled together, such that they each run in parallel in close proximity along their length of extension.

In some implementations, fiber 208 may be positioned in different arrangements. For example, in some implementations, fiber 208 may wrapped with a varying pitch, such that it wraps more frequently around certain portions relative to other portions. In some implementations, instead of a helical pattern, fiber 208 may be positioned such that it runs substantially parallel to the axial length of the drill collar 126. In some implementations, fiber 208 can be positioned according to any other arbitrary arrangement. In some implementations, fiber 208 can include combinations of two or more of these arrangements. For example, in some implementations, a fiber 208 can have a portion with a constant helical pattern, a portion with a parallel pattern, and a portion with a varying helical pattern.

In some implementations, signal source module 204 and signal detection module 206 may be placed on the same end of fiber 208, instead of on opposite ends. The signal detection module 206 may include an interferometer to analyze the spectrum of the reflected wavelengths of light in order to determine one or more thermomechanical properties.

The techniques described above can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For example, signal processing module 202 can include an electronic processor, and the electronic processor can be used to process optical signals detected by signal detection module 206 in order to determine one or more thermomechanical properties, as described above. In another example, the electronic processor can be used to control the operation of signal source module 204, signal detection module 206, and/or visualization module 212.

The term “electronic processor” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations, of the foregoing. The apparatus can include special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

In general, in an aspect, a system includes a bottom hole assembly (BHA) that includes one or more drill collars and a drill bit connected to the one or more drill collars. The system also includes a sensor system for monitoring the BHA. The sensor system includes one or more lengths of optical fiber helically wound and extending along the one or more drill collars, a signal source module arranged to emit an optical signal into the one or more lengths of optical fiber, a signal detection module arranged to detect the optical signal guided from the signal source module by the one or more lengths of optical fiber, a signal processing module in communication with the detection module, and an operator interface in communication with the signal processing module. The signal processing module is programmed to, during operation of the system, determine measurement information, based on the detected optical signal, about a thermomechanical property at multiple different locations on the one or more drill collars while the BHA is used to bore a well. The signal processing module is also programmed to, during operation of the system, send a signal to the operator interface when measurement information exceeds a threshold.

Implementations of this aspect may include one or more of the following features. The signal processing module may be further programmed to, during operation of the system, provide a recommendation to the operator interface based on the measurement information and the threshold. The thermomechanical property may be strain. The thermomechanical property may be temperature. The thermomechanical property may be pressure. The thermomechanical property may be a shape of the BHA. The BHA may include at least two drill collars connected to each other via a coupler, where the coupler includes a tube-shaped wall extending from a first end and a second end and a channel between the first end and the second end, and where the one or more lengths of optical fiber pass through the channel to continuously extend across the at least two drill collars and the coupler. The one or more lengths of optical fiber may be disposed in one or more channels that extend helically along the BHA. The system may further include a protective cladding disposed in the one or more channels. The signal source module may be positioned between the one or more drill collars and the drill bit. The system may further include a visualization module in communication with the signal processing module, where the visualization module is programmed to display the measurement information and an indication of a location that corresponds to the measurement information during operation of the system.

In general, in another aspect, a method of monitoring a bottomhole assembly (BHA) includes directing an optical signal into one or more lengths of optical fiber helically wound around and extending along one or more drill collars of the BHA, detecting the optical signal after the optical signal is guided by the one or more lengths of optical fiber, determining, based on the detected optical signal, measurement information about a thermomechanical property at multiple different locations on the one or more drill collars while the BHA is used to bore a well, and sending a signal to an operator interface when the measurement information exceeds a threshold.

Implementations of this aspect may include one or more of the following features. The method can further include providing a recommendation to the user based on the measurement information and the threshold. The thermomechanical property may be strain. The thermomechanical property may be temperature. The thermomechanical property may be pressure. The thermomechanical property may be a shape of the BHA. The method may further include displaying the measurement information and an indication of the locations on the BHA that corresponds to the measurement information.

In general, in another aspect, a sensor system for monitoring a bottom hole assembly (BHA) includes one or more lengths of optical fiber adapted to be helically wound and extended along a BHA, a signal source module arranged to emit an optical signal into the one or more lengths of optical fiber, a signal detection module arranged to receive the optical signal guided from the signal source module by the one or more lengths of optical fiber, a signal processing module in communication with the detection module, and an operator interface in communication with the signal processing module. The signal processing module is programmed to, during operation of the system, determine measurement information about a thermomechanical property at multiple different locations on the BHA , and send a signal to the operator interface when the measurement information exceeds a threshold.

Implementations of this aspect may include one or more of the following features. The signal processing module may be further programmed to, during operation of the system, provide a recommendation to the operator interface based on the measurement information and the threshold. The thermomechanical property may be strain. The thermomechanical property may be temperature. The thermomechanical property may be pressure. The thermomechanical property may be a shape of the BHA. The signal source module may be positioned between a drill collar and a drill bit. The system may further include a visualization module in communication with the signal processing module, where the visualization module is programmed to display the measurement information and an indication of the locations on the BHA that corresponds to the measurement information during operation of the system. The system may further include a coupler that connects a first portion of the BHA to a second portion of the BHA, where the coupler includes a tube-shaped wall extending from a first end and a second end and a channel between the first end and the second end, and where the one or more lengths of optical fiber pass through the channel to continuously extend across the at least two drill collars and the coupler.

A number of embodiments have been described. Other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A system, comprising: a bottom hole assembly (BHA) comprising one or more drill collars and a drill bit connected to the one or more drill collars; and a sensor system for monitoring the BHA, comprising: one or more lengths of optical fiber helically wound and extending along the one or more drill collars; a signal source module arranged to emit an optical signal into the one or more lengths of optical fiber; a signal detection module arranged to detect the optical signal guided from the signal source module by the one or more lengths of optical fiber; a signal processing module in communication with the detection module; and an operator interface in communication with the signal processing module, wherein the signal processing module is programmed to, during operation of the system: determine measurement information, based on the detected optical signal, about a thermomechanical property at multiple different locations on the one or more drill collars while the BHA is used to bore a well, and send a signal to the operator interface when measurement information exceeds a threshold.
 2. The system of claim 1, wherein the signal processing module is further programmed to, during operation of the system, provide a recommendation to the operator interface based on the measurement information and the threshold.
 3. The system of claim 1, wherein the thermomechanical property is strain.
 4. The system of claim 1, wherein the thermomechanical property is temperature.
 5. The system of claim 1, wherein the thermomechanical property is pressure.
 6. The system of claim 1, wherein the thermomechanical property is a shape of the BHA.
 7. The system of claim 1, wherein the BHA comprises at least two drill collars connected to each other via a coupler; wherein the coupler comprises a tube-shaped wall extending from a first end and a second end and a channel between the first end and the second end; wherein the one or more lengths of optical fiber pass through the channel to continuously extend across the at least two drill collars and the coupler.
 8. The system of claim 1, wherein the one or more lengths of optical fiber are disposed in one or more channels that extend helically along the BHA.
 9. The system of claim 8, further comprising a protective cladding disposed in the one or more channels.
 10. The system of claim 1, wherein the signal source module is positioned between the one or more drill collars and the drill bit.
 11. The system of claim 1, further comprising a visualization module in communication with the signal processing module, wherein the visualization module is programmed to display the measurement information and an indication of a location that corresponds to the measurement information during operation of the system.
 12. A method of monitoring a bottomhole assembly (BHA) comprising: directing an optical signal into one or more lengths of optical fiber helically wound around and extending along one or more drill collars of the BHA; detecting the optical signal after the optical signal is guided by the one or more lengths of optical fiber; determining, based on the detected optical signal, measurement information about a thermomechanical property at multiple different locations on the one or more drill collars while the BHA is used to bore a well; and sending a signal to an operator interface when the measurement information exceeds a threshold.
 13. The method of claim 12, further comprising providing a recommendation to the user based on the measurement information and the threshold.
 14. The method of claim 12, wherein the thermomechanical property is strain.
 15. The method of claim 12, wherein the thermomechanical property is temperature.
 16. The method of claim 12, wherein the thermomechanical property is pressure.
 17. The method of claim 12, wherein the thermomechanical property is a shape of the BHA.
 18. The method of claim 12, further comprising displaying the measurement information and an indication of the locations on the BHA that corresponds to the measurement information.
 19. A sensor system for monitoring a bottom hole assembly (BHA) comprising: one or more lengths of optical fiber adapted to be helically wound and extended along a BHA; a signal source module arranged to emit an optical signal into the one or more lengths of optical fiber; a signal detection module arranged to receive the optical signal guided from the signal source module by the one or more lengths of optical fiber; a signal processing module in communication with the detection module; and an operator interface in communication with the signal processing module, wherein the signal processing module is programmed to, during operation of the system: determine measurement information about a thermomechanical property at multiple different locations on the BHA , and send a signal to the operator interface when the measurement information exceeds a threshold.
 20. The system of claim 19, wherein the signal processing module is further programmed to, during operation of the system, provide a recommendation to the operator interface based on the measurement information and the threshold.
 21. The system of claim 19, wherein the thermomechanical property is strain.
 22. The system of claim 19, wherein the thermomechanical property is temperature.
 23. The system of claim 19, wherein the thermomechanical property is pressure.
 24. The system of claim 19, wherein the thermomechanical property is a shape of the BHA.
 25. The system of claim 19, wherein the signal source module is positioned between a drill collar and a drill bit.
 26. The system of claim 19, further comprising a visualization module in communication with the signal processing module, wherein the visualization module is programmed to display the measurement information and an indication of the locations on the BHA that corresponds to the measurement information during operation of the system.
 27. The system of claim 19, further comprising a coupler that connects a first portion of the BHA to a second portion of the BHA; wherein the coupler comprises a tube-shaped wall extending from a first end and a second end and a channel between the first end and the second end; wherein the one or more lengths of optical fiber pass through the channel to continuously extend across the at least two drill collars and the coupler. 